I. Field of the Invention
The present invention relates to collimators and components thereof for use in computed tomographic (CT) X-ray scanners and components thereof.
II. Background Information
A variety of fourth generation CT scanners require rotation of an X-ray source with simultaneous nutation of a detector ring. The nutation motion of the detector ring permits a clear path from the X-ray source to the oppositely positioned interior surface of the detector ring through movement of the near portion of the detector ring away from that path. A pre-patient collimator may be employed in conjunction with the X-ray source which comprises a slab or blade of beam stopping material having a longitudinal slot for passing X-rays from the source to the target area of the patient. However, the nutating motion of the detector ring results in a minimum amount of clearance between the collimator blade and detector ring in order to minimize the nutation angle at which the detector ring is tilted.
A pre-patient collimator constructed of a blade of X-ray beam stopping material having a longitudinal slot therein has been constructed by the inventors with the proximity of the slot to the lengthwise edge of the blade minimized in order to minimize the clearance between the collimator blade and the detector ring. However, the resultant narrow section of the collimator blade between the slot and detector ring has been found to vibrate. This vibration has been found to occur at fundamental frequencies which are typically on the order of 100 hertz. This means that the narrow section of the collimator blade might easily be driven into unacceptable vibration by normal gantry vibrations, thereby producing beam intensity modulation which will degrade image quality unless complex corrections are made.
It is, accordingly, an object of the present invention to provide a collimator which has a blade with a section narrow enough to minimize the nutation angle of a detector ring of a fourth generation CT scanner and yet avoid unacceptable vibration due to typical gantry vibrations.
Additional objects and advantages of the invention will be set forth in the description which follows and in part will be obvious from the description or may be learned by practice of the invention.